GB2055298A

GB2055298A - Tennis racquet

Info

Publication number: GB2055298A
Application number: GB7927580A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-07
Filing date: 1979-08-08
Publication date: 1981-03-04
Also published as: GB2055298B; US4196901B1; US4196901A; DE2932996A1; FR2464081B1; FR2464081A1; BE878431A

Abstract

A tennis racquet comprises a hand grip (14) having a length less than 40% of the total length of the racquet and a frame (10) having a generally elliptical bowed portion with ends comprising spaced throat portions (12, 12') and shaft portions (13, 13') extending to the hand grip, the ends being connected together only at the hand grip or at the hand grip and by a spacer (15) spaced from it and weighing less than 29 grams. The playing head occupies substantially all the area of the frame member, as limited by the spacer if present, and has interlaced longitudinal and transverse strings (17, 16), the tension in the longitudinal strings being about 5% to 25% greater than that in the transverse strings. <IMAGE>

Description

1 GB 2 055 298A 1

SPECIFICATION

Tennis racquets The invention relates to a tennis racquet. 70 It has been the practice over the years to construct tennis racquets with a generally el liptical or circular closed frame to which inter laced transverse and longitudinal strings are attached under substantial tension to provide a yieldable playing head. With wood-frame racquets, the handle, extending from the play ing head and terminating in a hand grip, was generally of solid construction, including a flared web or throat portion adjacent the play ing head. When a metal frame member of tubular,]-beam, or other appropriate cross sectional contour has been employed, it has been customary to rigidly join together the ends of the metal frame member at the han dle end of the playing head to complete the elliptical contour of the playing head and provide mounting means for the central longi tudinal strings.

Tennis racquets of these constructions have characteristically had a socalled---sweetspotin the playing head which is relatively small in comparison to the area of the playing head, and which is located considerably off center longitudinally, that is, in the direction of the handle of the racquet. The size and location of the -sweet spot- is of primary importance as this is the area in which a ball can be hit with maximum power and control. For it to be off- center toward the handle is doubly disadvantageous.

Firstly, the tendency is for a player to contact the ball, if possible, with the centre of the playing head, and only experts have the degree of control which enables that contact to be made consistently closer to the handle.

Secondly, the conventional racquet does not provide the range which its structural appearance would suggest when the player is playing hard-to-reach balls because the outer six inches or so of the playing head in the direction of the tip end of the racquet becomes progressively more "dead", and incapable of imparting speed to, and effecting control of, a ball being returned.

The invention provides a tennis racquet comprising a hand grip having a length less than 40% of the total length of the racquet, a frame member having a bowed portion of generally elliptical shape with ends comprising spaced throat portions extending from the bowed portion, and two shaft portions extending from the throat portions to the head grip, and interlaced longitudinal and transverse strings providing a playing head within the area of the frame member, the frame member ends being connected together only at the hand grip, and the playing head occupying substantially all the area of the frame mem- ber.

The invention also provides a tennis racquet comprising a hand grip having a length less than 40% of the total length of the racquet, a frame member having a bowed portion of generally elliptical shape with ends comprising spaced throat portions extending from the bowed portion and shaft portions extending from the throat portions to the hand grip, and interlaced longitudinal and transverse strings providing a playing head within the area of the frame member, the frame member ends being connected together by the hand grip and by a spacer spaced from the hand grip and weighing less than 29 grams, and the playing head occupying substantially all the area of the frame member as limited by the spacer.

The spacer of the tennis racquet of the invention can thus have a weight in the range of from 0 to 29 grams, being omitted or nonexistent at the lowest end of this range.

In a tennis racquet embodying the present invention, the---sweetspot", hereinafter referred to as low vibration area (L.V.A.) is significantly enlarged and extended toward the racquet tip. The percussion centre of the racquet is advanced toward the tip end of the racquet and the vibration level is reduced by reason of the reduced mass at the throat portion. The shape or peripheral contour of the generally elliptical head can be varied considerably while retaining this weight reduction in the central area of the racquet.

In the racquet of the invention, the stringed area as viewed with the racquet tip down has what might be called a - hanging drop- periphery, with the central longitudinal strings extending into the throat portion, and the centremost strings being secured to the frame at a point closer to the hand grip than they would in a purely elliptical contour. To compensate for the absence of sturdy transverse bracing in the throat portion of the racquet the longitudinal strings may be somewhat more highly tensioned than the transverse strings, preferably by about 5% to 25% higher tension in the longitudinal strings. This tends to spread and stiffen the frame at the throat portion, and the effect is enhanced by providing a divergence in the frame member ends between the hand grip and the elliptical bowed portion. This divergence can range from about 5' when the frame has a reversed curved throat forming portion, to about 30' when substantially straight throat and shaft portions tangentially join the elliptical bowed portion.

With the open throated construction several of the centre longitudinal strings will be longer than in a conventional racquet with a fully elliptical playing head, and the centre pair.of strings may be as much as about four inches.

A standard lightweight metal frame racquet of the popular 68.5 em length may weigh 2 GB 2 055 298A 2 approximately 370 grams. With the same materials, a racquet embodying the invention but otherwise similar will weigh approximately 340 grams. For many tennis players this weight reduction is attractive especially in net play.

The invention is further described below by way of illustration with reference to the accompanying drawing, in which:

Figure 1 is a plan view of a tennis racquet embodying the present invention; Figure la is a like fragmentary view of a racquet similar to that of Fig. 1 but having a modified hand grip structure; Figure 2 is a fragmentary sectional view on the line 2-2 of Fig. 1; Figure 3 is a fragmentary enlarged sectional view of the portion of the racquet of Fig. 1 indicated by the arrow 3 and showing a further modification; Figure 4 is a side view of the racquet shown in Fig. 1 having associated therewith a diagrammatic illustration of a first bending mode of the racquet; Figure 5 is a view similar to Fig. 4 having associated therewith a diagrammatic illustra tion of a second bending mode of the racquet; Figure 6 is a diagrammatic illustration of the low, medium and high vibration zones of a racquet in accordance with the prior art;

Figure 7 is a view similar to Fig. 6 but of the racquet of Fig. 11; Figure 8 is a view on a larger scale of the head portion of the racquet of Fig. 1 indicat ing a plurality of superimposed -minimum 100 vibration zones---; and Figure 9 is a composite view diagrammati cally indicating various weight placements as sociated with the racquet of Fig. 1.

The racquet shown in Fig. 1 comprises a frame 10 bowed to form a generally elliptical playing head portion 11 joined to elongate extensions including throat portions 12,12' and shaft portions 13,13' which are rigidly joined at their extremities by a hand grip 14. In the full line showing, the throat portions 12,12' have a reverse curvature, and the shaft portions 13,13', between the hand grip 14 and the throat portions, have a slight divergence, suitably of the order of W. The contour of the throat portions 12,12' can be considerably varied, however, to the extreme condition shown in broken lines in which the throat and shaft portions 12, 13 and 12', 131 are essentially straight or colinear, and have a divergence of as much as about 30' in tangentially joining the head portion 11.

The shaft portions 13,13' are rigidly joined together by a lightweight, metal or plastics spacer 15. The hand grip 14 is of conven- tional construction, having an outer wrap 141 of cushioning and slip resistant material but is of a length less than 40% of the total length of the racquet.

The playing head portion 11 has a plurality130 of transverse tensioned strings 16 interlaced with a plurality of longitudinal tensioned strings 17, and it will be noted that several of the central strings 17 extend into the throat portion of the racquet, with the centre pair of strings 17' being secured to the shaft portions 13,13' of the frame at points close to the spacer 15 or such that the strings 17' extend through the spacer.

The frame 10 can be fashioned from a variety of materials including wood, laminated wood plain or reinforced plastics, and metals of tubular and other cross sectional configurations. For purpose of illustration the frame 10 in Figs. 2 and 3 has been shown as having an 1-beam cross section with parallel cross members 18,18' in the plane of the racquet joined by a connecting web 19 perpendicular to this plane. The web 19 is provided with approxi- mately spaced apertures 20 for lacing of the strings 16, 17. To minimize abrasion of the strings passing through the apertures 20, these are preferably lined with cushioning members or bushings 21, suitably of plastic material.

Depending on the divergence of the shaft portions 13,13' the spacing of the frame at the anchorage points of the central longitudinal strings 17' may be greater than the de- sired spacing of strings 17, causing a slight divergence of the centre strings 17' as they approach the anchorage points. While this does not adversely affect the playing characteristics of the racquet the spacing of the centre strings 171 can, if desired, be adjusted by providing on the spacer 15 extensions 1 5a having string receiving passages 1 5b which align with apertures 20 in the web 19. In instances when strings adjacent the centre strings 17' would also be divergent if directly anchored to the frame, the extensions 1 5a can protrude along the web 19 to provide guide passages similar to passages 1 5b at the points of mounting of such strings. It should be noted, however, that any addition of weight in this portion of the racquet should be held to the minimum.

Fig. 1 is scaled to a standard 68.5 cm racquet, but the invention can be embodied in racquets of any size, including substantially shorter racquets, the spacer 15 may be omitted, as shown in Fig. 1 a in which event the hand grip 14 becomes the first rigid joist for the frame. In such a construction, the racquet frame will comprise simply the generally elliptical head and hand grip, and the hand grip can be a single shaft, which will still have a length which is less than 40% of the overall racquet length.

The absence of transverse bracing between throat portions 12,12' of the frame might seem to indicate a transverse weakness in this portion of the racquet, but any tendency toward this is offset by providing greater tension in the longitudinal strings 17 than in the transverse strings 16. The longitudinal tension should be at least 5% higher and suitably about 5% to 25% higher, depending in part on the degree of divergence in the throat and shaft portions 12,13 and 12', 13' of the frame. This added tension in the longitudinal strings imparts a spreading force to the frame which appears to effectively substitute for a heavy rigid connection in the throat portion.

The elimination of weight in the throat portion 75 is a key to the remarkably improved perfor mance of racquets embodying the present invention.

In Fig. 1, the percussion centre (P.C.), of the racquet has been shown as being in substantial alignment with the widest part of the head portion 11, with the LX.A. 22 extending a short distance toward the tip end of the racquet and a substantial distance to ward the hand grip end. The significance of the size and location of the L.V.A. 22 will be more fully understood from the following dis cussion.

Figs. 4 and 5 show an edge view of the racquet frame 10 and hand grip 14 of Fig. 1 and diagrammatically illustrate respectively first and second bending modes of the racquet frame. The scale of bending is much exaggerated for the sake of clarity, and it will be seen that the first bending mode is much like that of a diving board, with movement increasing regularly from the hand grip 14 to a maximum vibration 23 at the racquet tip. This is a relatively slow vibration of about 16 cps to 30 cps induced in the frame when force is applied at the racquet head and it induces no vibration in the hand grip 14, because the period of vibration is long compared to the duration of ball contact.

Force applied to the racquet at points above or below the P.C. induces the second bending mode shown in Fig. 5 in which the frame bends with respect to fixed points defined by the hand grip and the P.C., which is at approximately the node of this bending mode. The vibration at the tip as at 24, and between the hand grip and the P.C. as at 25 is very rapid, from 100 cps to 150 cps, and it is this bending mode which causes vibrations in the hand grip 14. Force applied at points above the P.C. generates the first and second bending moments, in phase with each other causing an additive effect and a more rapid increase in the amount of vibration with in- crease of distance of the point of impact GB 2 055 298A 3 above the P.C. than with increase of distance of the point of impact below the P.C.

In contrast to this, a ball hitting the racquet below the P.C. induces the second bending mode out of phase with the first with the result that there is a partial cancellation and less vibration is produced. This cancellation affects the size of the initial impulse.

In addition, analysis of the bending modes of a simple beam show the basic asymetry in 130 bending amplitude described previously, wherein the bending amplitude a given distance above the P.C. can be much larger than the bending amplitude the same distance be- low the P.C. This accounts for the fact that the L.V.A. as shown in Fig. 1 and in Figs. 6 and 7 extends a substantial distance below the P.C. and only a short distance above the P.C.

In considering Figs. 6 and 7, it must be realized that the low, medium and high vibration zones L, M, and H are not sharply defined, so the showing is diagrammatic. Low vibration in zone L is barely perceptible in the hand grip, medium vibration in zone M is perceptible but not very objectionable and high vibration in zone H is most objectionable for three reasons.

Firstly, in zone H much of the energy to be imparted to the ball is dissipated in racquet vibrations, hence the ball velocity when leaving the face of the racquet is considerably lower than when the ball leaves the LX.A. for the same overall angular velocity of the rac- quet, causing the ball to fall short of the player's intended range.

Secondly, the vibration frequency is high enough to cause multiple ball contact during a single stroke, hence the exact angular position of the face of the racquet is random at the moment the ball leaves the racquet. This causes the ball to take a direction which will generally not be the direction intended by the player.

Thirdly, the vibration force is transmitted through the frame of the racquet to the handle of the racquet and then to the arm of the player. This high vibration appears to be conductive to tendonitis and bursitis and other irritations commonly called -tennis elbow---.

In Fig. 6 there is shown the head of a conventional racquet having a frame in the form of a closed elipse 1 Oa. With this construction, the P. C. is not aligned with the widest part of the frame 1 Oa, but is substantially closer to the handle end of the frame, and zone L is quite small. A ball struck in the centre of the racquet head will be in zone M, and a substantial portion of the area of the playing head is in high vibration zone H.

In Fig. 7, which shows the racquet of Fig. 1 with an open throated frame 10, note that the P.C. is aligned substantially with the widest portion of the frame and zone L is substan- tially larger than in Fig. 6. This raises and enlarges zone M and in effect pushes most of zone H off the end of the racquet.

A comparison of Figs. 6 and 7 shows very closely why the racquet construction of the present invention not only enhances the useful area efficiency and precision of control of the playing head, but also enhances the comfort of the player by greatly reducing the amount of objectionable vibration which will be transmitted to the hand grip and thence to 4 GB 2 055 298A 4 the player's arm.

To understand the physics of this invention, reference should be made to the formula:

R = J/ M X r where R is the distance from base (hand grip end) of the racquet to the P.C., J is the moment of inertia of the racquet, M is the mass of the racquet, and r is the distance from the base of the racquet to the centre of gravity (C.G.).

By way of illustration, a racquet of 68.5 cm length as shown in Fig. 1 having a moment of inertia J of 614 kilogram CM2, a mass M of 340 grams and a distance r of 33 cm, has a distance R of 54.6 centimeters; and this is the approximate location of the P.C. on the rac quet.

In order to increase R we can alter the 85 weight distribution in the racquet.

R is most efficiently increased by removing weight in the vicinity of the centre of gravity, because, in that case, r, is essentially unal tered, M is reduced in direct proportion to the weight reduction, and J is only slightly reducd because each mass element contributes to J in proportion to the square of its distance from the centre of rotation.

R can be increased by the addition of 95 weight outbound of the centre of gravity, but this makes the racquet feel heavy to swing and unpleasant to use.

The effect of weight reductions at different locations, is better illustrated in Figs. 8 and 9.

In Fig. 8, which shows on an enlarged scale the playing head portion 11 of the racquet of Fig. 1 with parts identified by similar refer ence characters, 22a represents the minimum vibration area M.V.A. around the percusion centre P.C. of the racquet without modifica tion. Fig. 9 diagrammatically illustrates at a the unmodified racquet, and at b and c and d the effect of added weight at the locations and in the amounts indicated; the correspond ing minimum vibration areas are superim posed on Fig. 8 as 22b, 22c, and 22d.

In Fig. gb, which shows the addition of 29 grams at the C.G., the modified condition approximates to that of a conventional racquet of the same size, because the new construc tion has reduced the net mass in the general area of the C.G. by approximately 29 grams.

A comparison of 22a and 22b and the loca tions of the P.C. and the P.C.-b in Fig.

8 clearly shows the advantage of the new construction.

The weights shown in Figs. 9 c and 9 d permit ready visualization of the relative ef fects of different weight placements.

Various changes and modifications in the improved tennis racquet as herein disclosed may occur to those skilled in the art, and to the extent that such changes and modifica tions are embraced by the appended claims, it 130 is to be understood that they constitute part of the present invention.

Claims

1. A tennis racquet comprising a hand grip having a length less than 40% of the total length of the racquet, a frame member having a bowed portion of generally elliptical shape with ends comprising spaced throat portions extending from the bowed portion, and two shaft portions extending from the throat portions to the hand grip, and interlaced longitudinal and transverse strings providing a playing head within the area of the frame member, the frame member ends being connected together only at the hand grip, and the playing head occupying substantially all the area of the frame member.

2. A tennis racquet as claimed in claim 1 wherein the frame member throat portions have reverse curved contours between the shaft portions and the bowed portion.

3. A tennis racquet as claimed in claim 1 wherein the frame member throat portions are substantially straight and tangentially merge with the bowed portion.

4. A tennis racquet comprising a hand grip having a length less than 40% of the total length of the racquet, a frame member having a bowed portion of generally elliptical shape with ends comprising spaced throat portions extending from the bowed portion and shaft portions extending from the throat portions to the hand grip, and interlaced long- itudinal and transverse strings providing a playing head within the area of the frame member, the frame member ends being connected together by the hand grip and by a spacer spaced from the hand grip and weigh- ing less than 29 grams, and the playing head occupying substantially all. the area of the frame member as limited by the spacer.

5. A tennis racquet as claimed in claim 4 wherein the spacer is located between the centre of gravity of the racquet and the hand grip.

6. A tennis racquet as claimed in claim 4 or 5 wherein the frame member ends are of reverse curved contour between the spacer and the bowed portion.

7. A tennis racquet as claimed in claim 4 or 5 wherein the frame member ends are substantially straight between the space and the bowed portion and tangentially join the bowed portion.

8. A tennis racquet as claimed in claim 4, 5, 6 or 7 wherein the spacer includes spaced portions extending along the frame ends away from the hand grip, the spaced portions hav- ing means for guiding and spacing the central longitudinal strings at the points of attachment frame member.

9. A tennis racquet as claimed in any preceding claim wherein the tension in the longitudinal strings is greater than the tension GB2055298A 5 in the transverse strings to thereby enhance the transverse stiffness of the racquet in the region of the frame member throat portions.

10. A tennis racquet as claimed in claim 9 wherein the tension in the longitudinal strings is about 5% to 25% greater than the tension in the transverse strings.

11. A tennis racquet substantially as herein described with reference to Figs. 1, 2, 4, 5, 7, 8 and 9, Fig. 3, or Fig. 4 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess Ef Son (Abingdon) Ltd.-1 981. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.